A missile that is dropped from an airplane or fired from a large artillery piece so as to descend onto its target while suspended from a parachute can be provided with a target-sensing unit that explodes a charge in the missile when it approaches the target. This charge therefore lies behind a projectile- or shrapnel-forming layer with respect to the downward direction of travel of the missile, so that when it explodes this layer is propelled in the form of one or more pieces at the target. Such devices are particularly effective against armored vehicles which cannot penetrate by projectiles that have moved through a long distance and, therefore, lost most of their speed and momentum.
Typically the target-sensing device is a radar-like transmitter and receiver, most often one that detects the distance to the underlying ground so that the charge can be detonated at the optimum altitude, which is fairly low and impossible to detect accurately by a simple barometer-type altimeter. The device could also be a simple receiver that detonates as it approaches a signal-emitting target or beacon thereon.
As described in German Pat. No. 2,353,566 which corresponds to British Pat. No. 1,444,029, the target-sensing unit comprises at least one antenna for transmitting and receiving, a transmitter, a receiver, and circuitry connected between the transmitter and receiver and to the detonator in the charge when the target is appropriately sensed. At least the antenna of this unit is provided, relative to the normal direction of travel of the missile, in front of the charge and the element forming the secondary projectile or projectiles when the charge is detonated. Thus in a system wherein the lower surface is provided with a hard layer that breaks up and forms shrapnel, the energy of at least some of this shrapnel will be absorbed as it impacts the back of the target-sensing unit. Clearly this reduces the effectiveness of the secondary detonation.
The effective size of the antenna can be reduced as described in copending and coassigned application Ser. No. 628,751, filed on July 9, 1984 (now U.S. Pat. No. 4,584,943) connecting the antenna to the radar transceiver by means of a tubular waveguide centered on an axis parallel to the projectile travel direction. This waveguide is imbedded in the charge and is in fact also packed with explosive which itself can be a neutral dielectric. Such an arrangement has several advantages, but still does at least minimally block the forward face of the missile that becomes the secondary projectile or projectiles.